1. Field of the Invention
The present invention relates to perovskite mixed metal catalysts for the selective oxidation of ammonia (NH.sub.3) to nitric oxide (NO). Nitric acid is an industrial chemical of great commercial value. The production of nitric acid, its preparation from NO and its usefulness in industry is described by D. J. Newman in "Nitric Acid" in the Kirk-Othmer: Encyclopedia of Chemical Technology, 3rd Ed, Vol. 15, pgs. 853-871, published in 1981 and the references cited therein.
2. Description of the Relevant Art
An essential step in the manufacture of nitric acid is the catalytic oxidation of ammonia to nitric oxide and other nitrogen containing products. The present industrial process is a high-temperature operation using expensive noble metal catalysts. It is highly desirable to be able to replace these very expensive metal catalysts with low-cost, highly selective long-lived, mixed metal-oxide catalysts which possess high activity and selectivity for nitric oxide production.
The use of perovskites as catalysts for the conversion of nitrogen compounds to nitrogen and of organic compounds containing carbon and hydrogen to CO, CO.sub.2 and water, respectively, is generally discussed by R. J. H. Voorhoeve et. al. in "Perovskite Oxides: Materials Science in Catalysis" in Science, Vol. 195. No. 4281, pgs. 827-833, published Mar. 4, 1977; and also by R. J. H. Voorhoeve in Chapter 5, "Perovskite-Related Oxides as Oxidation Reduction Catalysts" in Advanced Materials in Catalysis J. J. Burton and R. L. Garten (eds) Academic Press: New York, P. 129 (1976).
Generally, perovskite catalysts have been used in the reduction of NO to N.sub.2 O and N.sub.2 to decrease the emission of NO into the atmosphere.
There have been only scattered, unconfirmed non-enabling fragmentary oral rumors of the possible use of a perovskite catalyst to selectively oxidize ammonia to nitric oxide, 2NH.sub.3 +5/2O.sub.2 .fwdarw.2NO+3H.sub.2 O, with a minimum of by-products, such as N.sub.2 O and N.sub.2.
S. Sekido, et al in European patent application No. 89,199 disclose perovskite-type oxide catalysts, for conversion of auto exhaust and combustion gases to CO.sub.2 and H.sub.2 O of the general form: EQU La.sub.(l-x)/2 Sr.sub.(l+x)/2 Co.sub.l-x M.sub.x O.sub.3
where M=Fe, Mn, Cr, V or Ti and x is between 0.15 and 0.90. The quantities of HC, CO and NO in a combusted city gas treated with the perovskite catalyst were reduced.
In U.S. Pat. No. 3,884,837, J. P. Remeika et al. disclose mixed metal oxide catalysts having perovskite-like structures for the conversion of NO.sub.x pollutants to N.sub.2 O, N.sub.2 and O.sub.2.
In U.S. Pat. No. 3,888,792, D. O. Hughes discloses the formation of shaped bodies for catalysts in industrial processes. A catalyst in the form of a shaped body has adequate mechanical strength for use in industrial processes. The catalysts are prepared by co-precipitating from solution as carbonates or basic carbonates cobalt and at least one of the elements of the oxides, washing and drying the precipitates. The dried precipitate is heated between 250.degree. and 450.degree. C. for a time sufficient to convert the carbonates to their respective oxides, comminuting the mixture of oxides, shaping the mixture into bodies and heating the shaped bodies in the range of 600.degree. to 850.degree. C. The catalysts obtained were tested using an ammonia oxidation reactor. The oxidation efficiency of the perovskite catalyzed reaction of ammonia to nitric oxide was measured at various gas rates over the shaped body catalysts at a catalyst bed temperature of 650.degree. C. using an ammonia/air mixture having a volume ratio 1:10 ammonia/air.
In U.S. Pat. No. 4,018,712, T. P. Li discloses an improved catalyst for the oxidation of ammonia to nitric oxide. The catalyst contains the elements: antimony, uranium, iron, bismuth and molybdenum, and optionally, nickel or cobalt. The method of preparing the catalyst and the catalytic oxidation conditions are disclosed.
In U.S. Pat. No. 4,082,837, J. M. Whelan discloses a process for the selective oxidation of ammonia to nitric oxide in the presence of a variety of ceramic catalysts. The ammonia is passed over a ceramic catalyst having an empirical formula at elevated temperature of W.sub.K X.sub.N J.sub.(l-K-N) ZO.sub.(3+OR-M) where W is zirconium, tin, or thorium or mixtures thereof; X is an alkaline earth metal or mixtures thereof; J is scandium, Yttrium, a rare-earth element or a mixture thereof; Z is a metal of the first transition series or a mixture thereof, at least 0.01% of said metal having an oxidation state other than +3. K is a number having a value between 0 and about 0.1; M is a number having a value of from 0 to about 0.26; and N is a number from 0 to about 0.51 provided that when N has a value of 0, K has a value of between 0 and 0.05.
In U.S. Pat. No. 4,124,687, J. M. Whelan similarly discloses a process for the selective oxidation of ammonia to nitric oxide at temperatures of 100.degree.-400.degree. C. in the presence of ceramic catalysts.
In U.S. Pat. No. 4,126,580, A. Lauder discloses a number of perovskite mixed metal catalysts for use in oxidation of hydrocarbons and reduction of NO to N.sub.2 of the general formula: ABO.sub.3, where A and B are specific metal atoms. The surface area of these perovskites is low.
In U.S. Pat. No. 4,134,852, T. E. Volin discloses a high energy impact method to formulate mixtures of metal compounds as powders, followed by treatment with heat. Catalytic materials having a general empirical formula: ABO.sub.3, and a perovskite-type crystal structure are obtained.
In U.S. Pat. No. 4,189,405, A. G. Knapton et al. disclose the preparation of a number of mixed metal oxide catalysts for use in a deposition on metallic shaped articles.
In U.S. Pat. No. 4,363,361, A. J. Madgavkos et al. disclose the oxidation of carbon-containing compounds using perovskite-type crystal structure.
In U.S. Pat. No. 4,389,339, L. E. James, et al., disclose the preparation of a ceramic cobalt oxide/cobalt nitrate catalyst to oxidize ammonia to nitric oxides. This particulate cobalt oxide catalyst has high activity and improved resistance to disintegration and improved ammonia oxidation.
None of the above references individually or together disclose or suggest the present invention which is the preparation of certain perovskite catalysts having a certain range of lattice oxygen binding energies and/or high surface area of between about 20 to 50 meters.sup.2 /gram or greater or the use of these and other perovskite catalysts to selectively oxidize ammonia to nitric oxide.